1. Field of the Disclosure
The present disclosure relates to a capacitance detecting device which performs offset adjustment in the process during which converts minute changes in capacitance detected through a capacitance-type sensor into charge, and transmits the charge to an integrator.
2. Description of the Related Art
In related art, there is a capacitance detecting device (Japanese Unexamined Patent Application Publication No. 2007-3300) which detects minute changes in capacitance through a capacitance-type sensor, converts the amount of change of the detected capacitance into charge using a charge reading mechanism, transmits the charge read by the charge reading mechanism to an integrator, and integrates the transmitted charge, thereby converting the charge into a voltage signal. A capacitance component (hereinafter referred to as “offset”) other than the inherent capacitance to be detected is included in the charge read from the capacitance-type sensor by the charge reading mechanism and transmitted to the integrator. It is desirable to remove the offset in the process during which charge is transmitted to the integrator from the charge reading mechanism.
An offset adjustment circuit for charge extraction (or injection) can be provided in a line which transmits charge to the integrator from the charge reading mechanism. The offset adjustment circuit includes a variable capacitance element which has one end connected to the charge transmission line which transmits charge and can apply a driving pulse from the other end. In synchronization with an integral action (charge transmission to the integrator from the charge reading mechanism), a driving pulse is added at each integration, and the charge equivalent to the offset is extracted from the transmission charge. The resolution of the variable capacitance element included in the offset adjustment circuit is determined by the synthetic capacitance of a plurality of capacitative elements for adjustment which constitutes the variable capacitance element. The number of the capacitative elements for adjustment is selected, and the charge equivalent to the synthetic capacitance is extracted as offset in the variable capacitance element.
However, individual capacitors which constitute the variable capacitance element have a limit on realizing smaller capacitance due to restrictions of a semiconductor process. For this reason, there is also a limit on the precision of the capacitance by which the offset adjustment circuit extracts (or injects) in the variable capacitance element in one integral action, and sufficient resolution is not necessarily realizable.